Often, fasteners used to assemble performance critical components are tightened to a specified torque level to introduce a “pretension” in the fastener. As torque is applied to the head of the fastener, the fastener may begin to stretch beyond a certain level of applied torque. This stretch results in the pretension in the fastener which then holds the components together. Additionally, it is often necessary to further rotate the fastener through a specified angle after the desired torque level has been applied. A popular method of tightening these fasteners is to use a torque wrench.
Torque wrenches may be of mechanical or electronic type. Mechanical torque wrenches are generally less expensive than electronic. There are two common types of mechanical torque wrenches, beam and clicker types. In a beam type torque wrench, a beam bends relative to a non-deflecting beam in response to applied torque. The amount of deflection of the bending beam relative to the non-deflecting beam indicates the amount of torque applied to the fastener. Clicker type torque wrenches have a selectably preloaded snap mechanism with a spring to release at a specified torque, thereby generating a click noise.
Electronic torque wrenches (ETWs) tend to be more expensive than mechanical torque wrenches. When applying torque to a fastener with an electronic torque wrench, the torque readings indicated on the display device of the electronic torque wrench relate to the pretension in the fastener due to the applied torque. Some ETWs are also capable of measuring angular rotation of the wrench, and therefore the fastener, in addition to measuring the amount of torque initially applied to the fastener. However, fasteners are often positioned such that both the torque and the desired additional angular rotation may not be applied with the torque wrench in a single, continuous motion. In such cases, an electronic torque wrench having a ratcheting feature can be used.
An electronic torque wrench capable of angle measurement during ratcheting operations may begin measuring and accumulating the angular rotation of the ETW the moment the user begins to rotate the ETW. The instant initiation of angular measurement can lead to inaccuracies due to “play” found in the wrench's ratcheting mechanism that causes the ETW to rotate slightly prior to the actual rotation of the fastener. These inaccuracies are compounded where the angular rotation cannot be achieved in a single rotary motion of the ETW. Consider, for example, if such an ETW rated for 100 ft-lbs is used to rotate a fastener through a 90° angle, wherein the fastener's position restricts the ETW's rotation to 30° and the accumulation of the angular rotation begins immediately upon the ETW's rotation. As shown in the graph of FIG. 1A, as the first 30° of rotation subsequent to reaching the previously-applied target torque, that being 10 ft-lbs in the present example, are applied to the fastener, the amount of the ETW's angular rotation is measured from 0 ft-lbs of torque up to the maximum torque applied to the fastener during the first cycle, for example 20 ft-lbs. The ETW's measured angular rotation during the first cycle is represented by the entire solid line portion of the graph, indicated by portions 102 and 103. Because the fastener will only rotate after the ETW exceeds the previously-applied torque of 10 ft-lbs, angular rotation should only be measured and accumulated for solid line portion 102, as any angular rotation measured over solid line portion 103 is merely due to “play” in the ratcheting mechanism, deflection of the ETW body, etc.
In the second cycle, the ETW rotates through an additional 30°, reaching a new maximum torque value of 50 ft-lbs. As in the first cycle, the angular rotation measurement begins immediately upon the ETW's rotation. However, the fastener does not actually rotate until the ETW reaches the previous cycle's maximum applied torque of 20 ft-lbs. As such, any deflection of the ETW unit or play in the ratcheting mechanism that may occur between 0 ft-lbs and 20 ft-lbs, as represented by portion 105 of the graph, is erroneously added to the accumulated angular rotation value, whereas angular rotation should only be accumulated between 20 ft-lbs and 50 ft-lbs, as represented by portion 104 of the graph. Similarly, for the third cycle, any deflection of the ETW unit or play in the ratcheting mechanism that may occur between 0 ft-lbs and the previous cycle's maximum applied torque of 50 ft-lbs, as represented by portion 107 of the graph, is erroneously added to the accumulated angular rotation value, whereas angular rotation should only be accumulated between 50 ft-lbs and 100 ft-lbs, as represented by portion 106 of the graph. Similar inaccuracies can occur with each subsequent ratcheting cycle.
To help prevent inaccuracies due to play in the ETW's ratcheting mechanism, deflection of the ETW body, etc., some ETWs begin measuring and accumulating angular rotation at a fixed percentage of the torque wrench's rated capacity, such as 5%. Using such a fixed percentage to initiate angular measurement can also lead to inaccuracy, however, where a desired angular rotation cannot be achieved in a single rotary motion of the ETW. Consider, for example, if such an ETW rated for 100 ft-lbs is used to rotate a fastener through a 90° angle, wherein the fastener's position restricts the ETW's rotation to 30° and the accumulation of the fastener's angular rotation begins only after the ETW applies 5 ft-lbs of torque (i.e. 5% of its rated capacity). As shown in the graph of FIG. 1B, as the ETW rotates the first 30° subsequent to reaching the previously-applied target torque, that being 10 ft-lbs in the present example, the ETW measures angular rotation from 5 ft-lbs of torque up to a maximum torque applied during the first cycle, for example 20 ft-lbs. The fastener's angular rotation during the first cycle is represented by the solid line portion of the graph, indicated by 112. Unlike the example shown in FIG. 1A, the 5 ft-lbs threshold for measuring and accumulating angular rotation helps prevent some of the inaccuracies in angle accumulation during the first ratcheting cycle, more specifically, those that occur between 0 ft-lbs and 5 ft-lbs. However, the ETW begins measuring angular rotation at the 5 ft-lbs threshold, whereas the fastener does not actually rotate until the ETW reaches the previously-applied target torque of 10 ft-lbs. As such, the ETW erroneously accumulates any deflection that may occur between the previously-applied torque of 10 ft-lbs and the 5 ft-lbs threshold, as represented by portion 113 of the graph.
In the second cycle, the ETW rotates through an additional 30°, reaching a new maximum torque value at 50 ft-lbs. As in the first cycle, the ETW begins measuring angular rotation at 5 ft-lbs of applied torque. However, the fastener does not actually rotate until the ETW reaches the previous cycle's maximum applied torque of 20 ft-lbs. As such, the ETW erroneously accumulates any deflection that may occur between the applied torques of 5 ft-lbs and 20 ft-lbs, as represented by portion 115 of the graph, whereas angular rotation should only be accumulated between 20 ft-lbs and 50 ft-lbs, as represented by portion 114. Similarly, for the third cycle, the ETW erroneously accumulates any deflection of the ETW that may occur between the applied torque of 5 ft-lbs and the previous cycle's maximum applied torque of 50 ft-lbs, as represented by portion 117 of the graph, whereas angular rotation should only be accumulated between 50 ft-lbs and 100 ft-lbs, as represented by portion 116. Similar inaccuracies can occur with each subsequent ratcheting cycle.
The present invention recognizes and addresses certain or all of the foregoing considerations, and others, of prior art constructions and methods.